Class Notes (1,100,000)

CA (630,000)

U of A (10,000)

CHEM (1,000)

CHEM101 (200)

Yoram Apelblat (90)

Lecture 4

This

**preview**shows half of the first page. to view the full**1 pages of the document.**CHEM 101 - Lecture 4 - Bohr Model and Quantum Theory

Note: Read sections 7.4, 8.1.

Practise problem set 2, questions 1 - 4

Bohr Model for Hydrogen Atom:

● Hydrogen atom is the simplest atom

● Classical mechanics predicts that the electron would collapse into the positive nucleus,

contrary to observations.

● Bohr’s model blends classical and quantum theories.

○ There is one (and only one) electron moving in a circular orbit around the

nucleus.

○ The electron has only a fixed set of allowed orbits.

○ The electron can only have a certain finite energies (also known as quantums)

○ En= -Rh (z2/ h2)

■ R = Rydberg’s constant = 2.178 x 10-18 J

■ Z = Nuclear charge = number of protons = atomic number

■ n = integer value, beginning at 1, going to infinity. n cannot equal 0

■ So for hydrogen, Z = 1

■ For He+ Z = 2, Li 2+ Z= 3

■ radius of an orbit = a x n2 where a=0.053 nm (This explains how each

subsequent orbit gets further and further away from the nucleus)

■ Ex. for n=1: E1 = -Rh x Z2 < 0 (This will be a negative value)

■ Ex. for n = infinity: E = -Rh x( Z2/

∞

2) = 0

■ For absorption: Change in energy is a positive value

■ For emission: Change in energy is a negative value

■ Change in energy and wavelength is inversely proportional

Atomic Spectra: Hydrogen and Hydrogen like Atoms

● H atom: 1 electron, one proton, z = 1

● Bohr model: 1 electron orbits around a nucleus

● H -like atoms are really ions

○ Ex. He has 2 electrons and 2 protons, which does not conform to the Bohr

model.

○ However, He+ has 1 electron, 2 protons, Z = 2. This follows Bohr’s model.

○ Li 2+ has 1 electron, 3 protons, z =3. This follows Bohr’s model.

○ Li and Li+ will not work because there is more than one electron orbiting around

the nucleus.

● General formula for H - like atom: E+ (Z -1)

○ Only certain energy levels are allowed.

○ =

###### You're Reading a Preview

Unlock to view full version

Subscribers Only